The present invention relates to a process and more particularly to the separation and the recycling of catalyst components from a chemical reaction mixture.
A process for the separation and recycling of catalyst components from a chemical reaction mixture is disclosed. The process entails at least one extraction step.
Quaternary salts, for example tetraalkylammonium or tetraalkylphosphonium salts, are utilized in many reactions as a phase transfer catalyst, as a conducting electrolyte or in other functions. Because these compounds are costly it is important for the economics of industrial production processes that the quaternary salts are recovered from the reaction mixtures so that they can be re-utilized.
It is known (EP A1 913 197, U.S. Pat. No. 6,310,232, Handbook of Phase Transfer Catalysis, Y. Sasson, R. Neumann, editors, Blackie Academic, London 1997, p. 127 et seq.) that quaternary salts can be extracted from organic phases by means of water.
An example of the use of quaternary salts is diaryl carbonate production by oxidative direct carbonylation of aromatic hydroxy compounds in the presence of CO, 02 and a precious metal catalyst (see, for example, DE-A 27 38 437, U.S. Pat. No. 4,349,485, U.S. Pat. No. 5,231,210, EP-A 0 667 336, EP-A 0 858 991, U.S. Pat. No. 5,760,272). Palladium is preferably utilized as the precious metal. A co-catalyst (for example manganese salts or cobalt salts), a base, a quaternary salt, various quinones or hydroquinones and drying agents can additionally be dispensed-in. It is possible here to work in a solvent.
After the reaction has been carried out, product mixtures which comprise, inter alia, a hydroxyaromatic compound B, one or more quaternary salts A, reaction products C such as, for example, water and diaryl carbonates, as well as possibly solvent, further catalyst components, auxiliary substances and impurities, are obtained in these reactions. The object here is to separate one or more products C from the quaternary salts A and to return A into the reaction, as far as possible without impurities which are comprised in the reaction mixture.